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Review Article pISSN 2383-5389 / eISSN 2383-8116 Journal of International Society for Simulation 2015;2(2):58-63 http://dx.doi.org/10.18204/JISSiS.2015.2.2.058

Image-guided Stereotactic : Practices and Pitfalls

Na Young Jung, M.D., Minsoo Kim, M.D., Young Goo Kim, M.D., Hyun Ho Jung, M.D.,Ph.D., Jin Woo Chang, M.D.,Ph.D., Yong Gou Park, M.D., Ph.D., Won Seok Chang, M.D. Department of Neurosurgery, Research Institute, Yonsei Medical Gamma Knife Center, Yonsei University College of Medicine, Seoul, Korea

Image-guided neurosurgery (IGN) is a technique for localizing objects of surgical interest within the brain. In the past, its main use was placement of electrodes; however, the advent of computed has led to a rebirth of IGN. Advances in comput- ing techniques and tools allow improved surgical planning and intraoperative information. IGN influences many neurosurgical fields including neuro-oncology, functional disease, and . As development continues, several problems remain to be solved. This article provides a general overview of IGN with a brief discussion of future directions. Key WordsZZStereotactic ㆍNeurosurgery ㆍNeuro-image ㆍPitfall.

Received: November 26, 2015 / Revised: November 27, 2015 / Accepted: December 7, 2015 Address for correspondence: Won Seok Chang, M.D. Department of Neurosurgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea Tel: 82-2-2228-2150, Fax: 82-2-393-9979, E-mail: [email protected]

Introduction to approach deep structures in the brain and, perform , injection, stimulation, implantation, or radiosurgery. In mod- Stereotactic neurosurgery (SNS) is a minimally invasive sur- ern times, brain structures are virtualized in real time, leading gical procedure for diagnosis and treatment of brain , to developments in treatment and functional neu- that relies on locating targets relative to an external frame of ref- rosurgery. Most stereotactic procedures are conducted with an- erence. Stereotactic is a compound of “stereo” from the Greek atomical targeting based on brain atlases and neuroimaging, “three-dimensional” and “tactus” from Latin “to touch” (1). The so technological advancements have great importance. object of is to actually touch the targeted The aim of this study is to give an overview of current prac- structure by moving electrodes or probes along three axes, an- tices and pitfalls of IGN and suggest future directions. terior-posterior (AP), lateral, and vertical planes. Since Ernest A. Spiegel and Henry T. Wycis developed the first stereotactic hu- Imaging Modalities for IGN man apparatus in 1947, surgical instruments have advanced along with neuroimaging technology and neurophysiology (2). Initial development of IGN was rapid. Ventriculography and Compared to other surgical fields, brain surgery limits the ac- established anatomical references, quisition of anatomical information by vision or touch alone. such as the anterior-commissure (AC) and posterior-commis- Target structures are relatively small and more deeply seated sure (PC) line. These two landmarks supported the develop- than in other organs, providing narrow working space to sur- ment of the main atlases of the (1, 3, 4). Cerebral geons. Accordingly, early surgical risks were usually high. New showed the three-dimensional characteristics of surgical methods offered safer and more precise approaches the cerebral vasculature and its relationship with intracranial via small or even blind fashion. In particular, introduction of im- lesions, especially in tumor or vascular malformations. IGN age-guided neurosurgery (IGN) in the late 1970s made it possible underwent a second revolutionary change after computed to-

58 Image-guided Stereotactic Neurosurgery █ Jung NY, et al mography (CT) scans became available in clinics. CT provides disorders such as obsessive-compulsive disorder, depression, direct visualization of intracranial structures and accurate ste- and Tourette syndrome. In the past, lesioning procedures were reotactic localization due to its reduced image distortions. CT popular, but DBS became preferred because of its reversibility has negative features such as low image resolution, susceptibility and adjustability. DBS provides electrical stimulation to specif- to metal artifacts, and a high x-ray radiation load to the patient. ic functional targets by inserting electrodes into deep brain struc- Magnetic resonance imaging (MRI) presented exquisite ana- tures related to motor or limbic circuits. tomical information in three directional axes (axial, sagittal, cor- In DBS, localization depends anatomical and physiological onal). It had high image resolution, making it possible to visual- targeting. Anatomical localization uses the connecting line be- ize the vessels with gadolinium contrast. There were, however, tween the AC and PC as a reference. Three-dimensional coor- shortcomings: image distortions, relatively long scan times, and dinates (X, Y, Z) are used to target a point based on the brain at- potential hazards associated with implanted devices. In the mod- las. Visible structures from CT or MRI scans are then combined ern era, multimodal imaging began to use fusion techniques to match the target (Fig. 1). Physiological localization also helps based on contours, image intensity and voxel matching. These in identifying different basal ganglia and thalamic nuclei on the merged data allowed more available information about basis of electrophysiological properties. As physiological targets their patients. Furthermore, frameless stereotactic navigation are generally not visible on neuroimages, the typical firing pat- systems are now available for minimally invasive real-time lo- tern of each target is used to recognize accurate placement of calization. the electrode and predict side effects of electrical stimulation. In summary, whole DBS procedures are performed under the Current Practice of Stereotactic IGN combination of atlas-based, image guided targeting and elec- trophysiological monitoring through microelectrode recording (DBS) (MER). Deep brain stimulation (DBS) is a well-known neuromodula- PD is the main indication of DBS, especially in patients with tion therapy for a wide range of clinical fields. It is used to treat dopamine-resistant symptoms, motor fluctuations, and levodo- movement disorders, such as Parkinson’s disease (PD), essen- pa-induced dyskinesia (5, 6). The subthalamic nucleus (STN) is tial tremor (ET), and dystonia, as well as refractory psychiatric a key structure in the basal ganglia-thalamo-cortical motor cir-

Fig. 1. Preoperative planning of deep brain stimulation in a patient with Parkinson disease (Leksell SurgiPlan®, Elekta AB, ). Brain images of axial, coronal and sagittal magnetic resonance imaging and computed tomography show not only target points at the bilateral subthalamic nucleus but also the entry point and, insertion trajectory.

www.issisglobal.org 59 Journal of International Society for Simulation Surgery █ 2015;2(2):58-63 cuit, and DBS of the STN showed striking improvements, of DBS requires a high degree of accuracy because a tiny error, 41-55%, in motor function (5, 7-10). The inter- even 2-3 mm, can cause critical problems in patients. IGN has nus (GPi) is also an important stimulation target, demonstrat- improved neurosurgical outcomes through stereotactic tech- ing similar improvements in motor symptoms to STN DBS. niques, yet, further study is necessary to overcome unsolved GPi DBS has also been helpful in several types of dystonia, par- technical issues and ensure better outcomes. ticularly primary dystonia related to DYT1 gene mutation (11, 12). In ET, patients suffer from severe tremor that impairs daily life. Gamma knife radiosurgery (GKRS) DBS of the ventrointermediate nucleus (Vim) of the Radiosurgery developed by as a non-invasive tech- showed remarkable reductions (75-90%) in tremor score, im- nique to destroy intracranial disorders with single, high-dose proving quality of life (13-16). In patients with psychiatric dis- ionizing beams (19). Technical developments were thereafter orders, DBS can be targeted to white matter tracts in the ante- achieved in the domain of radiosurgery devices and radiation rior limb of the internal capsule (ALIC), ventral capsule (VC), sources, as well as surgical aspects such as irradiation technol- and inferior thalamic peduncle (ITP), as well as to gray matter ogy and dose planning. In contrast to conventional radiothera- structures in the ventral striatum (VS), nucleus accumbens (NAc), py, gamma knife radiosurgery (GKRS) precisely delivers highly and STN (5, 17, 18) fractionated radiation focusing multiple beams on a defined tar-

Fig. 2. Stereotactic gamma knife surgery in 37-year-old woman with arteriovenous malformation on right frontal lobe (volume 15.2 mL, maximal dose 28 Gy).

60 Image-guided Stereotactic Neurosurgery █ Jung NY, et al get volume under stereotactic conditions (Fig. 2). Normal tissue Magnetic resonance-guided focused ultrasound around the target receives minimal dose due to the small field (MRgFUS) size and sharp dose fall-off of radiosurgery (20). Radiation ef- Magnetic resonance-guided focused ultrasound (MRgFUS) fects at cellular level are mostly direct DNA damage, and le- is a non-invasive lesioning procedure using focused ultrasound sions produced by free radicals. Patients wear a frame on their and frame- and image-based guidance. Thermal can heads while scanned by MRI, then target points are established be performed when energy from high-intensity acoustic waves in treatment planning software based on imaging modalities is absorbed by target tissues (31). It can also cause inertial cavi- like MRI, CT, positron emission tomography (PET), and angi- tation (32). Because energy absorption in the ultrasound beam ography. Patients can be treated in a minimally invasive fashion path is low, surrounding normal tissue is spared. MRgFUS en- and return to usual activities the next day. GKRS has found ap- ables ultrasonic energy to be focused through the intact skull, al- plications as a primary strategy or adjuvant therapy in a number lowing application in and functional neurosur- of clinical fields including intracranial tumors, vascular malfor- gery, such as for ET and, subthalamotomy for mations, psychiatric disorders, and functional disorders such PD (33-35). Another potential approach in cases of central ner- as pain, movement disorder, and (21-25). Despite risks vous system (CNS) tumor disrupts the blood-brain barrier (BBB) of radiation-induced adverse effects, GKRS is now an indispens- and delivers therapeutic agents directly into the brain. MRgFUS able neurosurgical tool, especially in cases where the is too has a major benefit in its non-invasiveness, as well as less side hard to approach with standard neurosurgery and the patient’s effects compared with other lesioning modalities like radiofre- condition not good enough to endure open surgery (26). quency procedure or GKRS. Additionally, accuracy can be mon- GKRS must be precise to prevent serious adverse biological itored during procedures via real-time, closed-loop monitoring events. Advancement in neuroimaging and image-guidance of MR thermometry and sequential MR images. Currently, tem- techniques are thus essential to the safety and effectiveness of perature increase is the main factor associated with successful GKRS. results, and, studies identify skull volume and skull density ratio as important factors affecting thermal rise during MRgFUS (36). Stereoelectroencephalography (SEEG) implantation MRgFUS is one of the most outstanding surgical techniques. Stereoelectroencephalography (SEEG) is a safe and accurate It is purely image-guided, not coordinate-guided surgery. Con- method of invasive recording used to identify the epileptogenic sequently, more accurate neuroimaging guidance is indispens- zone (EZ) in some patients with medically refractory epilepsy, able for targeting small, deeply located structures. Although low particularly in surgical cases where noninvasive investigations spatial resolution and signal-to-noise ratios (SNR) are limiting like scalp electroencephalography and, imaging tools have factors, continuous study of these issues is expected to contrib- failed (27). SEEG is a stereotactic technique for implantation of ute to broad application of MRgFUS. Clinical and experimental multilead electrodes in suspicious intracerebral structures trials are proceeding on optimal indications and favorable out- based on a working hypothesis from analysis of noninvasive comes of these new procedures. data. SEEG can be combined with thermocoagulation to lesion a targeted area for treatment (28). It permits precise recordings Pitfalls and Trouble Shootings in IGN of deep-seated structures, bilateral explorations, or maps of ic- tal onset and propagation. In addition, it avoids large cranioto- Although stereotactic procedures attempt to be as accurate as mies compared with subdural electrodes. Stereotactic implan- possible in positioning the electrode at target points, position- tation is performed following the Talairach method (29). ing may actually be incorrect because of brain shifting, device Preoperative planning should always consider the accurate tar- error, surgical mistakes, or image related factors. Stereotactic geting of the desired brain structures and avoid the risk of in- neurosurgeons have attempted to overcome these problems. tracranial or cortical vessel injury. According to circumstances, Particularly in invasive procedures, they concentrate on allow- it may require not only basic MRI images but also functional ing as little cerebrospinal fluid (CSF) leakage as possible and MRI, and diffusion tensor imaging to preserve functionally pay special attention to diuretics use or hyperventilation (37). critical structures (30). Recently, SEEG has been updated with IGN is a blind practice, the most fearful complication of which high-resolution neuroimaging and robotic stereotactic systems. is intracranial hemorrhage, reported as approximately 1.5-2.2% Constant technological efforts are vital to decrease safety and per lead and 2.6-4.3% per patient (38, 39). To prevent this, ste- accuracy issues. reotactic surgeons use image-guided trajectory planning be- fore electrode insertion, planning pathways to avoid blood ves-

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